Pathogenic TP53 gene variants underlie 70% of Li-Fraumeni Syndrome (LFS), a hereditary cancer syndrome classically associated with predisposition to multiple primary neoplasms, particularly sarcoma, brain, breast, adrenocortical and other malignancies at unusually early ages. Traditionally, clinical TP53 testing was limited to individuals and families who met specific criteria. With the introduction of NGS-based multi-gene panel testing (MGPT), TP53 testing is now being performed on large numbers of people who do not meet LFS criteria. Broader MGPT testing for TP53 mutations has raised concerns about:1) a broader phenotypic spectrum for mutation carriers; and 2) the clinical relevance of TP53 variants identified in blood or saliva with allele frequencies below the 50% expected frequency for a germline carrier. We demonstrated that aberrant clonal expansions (ACE) of hematopoietic cells (clonal hematopoiesis CH) with an acquired pathogenic TP53 variant is responsible for many such cases. ACE/CH, which is observed at increasing frequency with advancing age in healthy populations, and after exposure to chemotherapy in cancer survivors, has been associated with increased risk of hematologic malignancy. Clinically, it is critical to discern true germline from somatic TP53 variants (ACE), since the clinical implications differ substantially. Carriers of true germline TP53 mutations may bear the psychological, medical and financial costs of striking personal and family cancer risks, the burden of intensive surveillance, the high risks of cancer deaths at disproportionately young ages and the weight of possibly passing TP53 variants to offspring. Those with ACE/CH may be followed for increased risk of hematologic malignancy or heart disease. More research is needed to better quantify TP53 associated risks to clarify optimal management. The investigators will partner with colleagues from the Li-Fraumeni Exploration Consortium (LiFE), and others with patients ascertained through broader, more agnostic approaches to testing: commercial genetic testing laboratories, the Geisinger MyCode project, the PROMPT study of individuals with germline mutations, and the ORIEN tumor/germline sequencing project, to assemble the largest cohort of individuals with a TP53 mutation in blood or saliva and their relatives. Given the rarity of LFS, acquiring this cohort through other means would be cost prohibitive and impracticable. In aim 1, we will estimate the TP53-related site-specific cancer risks in families identified through agnostic testing approaches and study tumor genomic characteristics in their collected tumor specimens. In aim 2, we will investigate the roles of TP53 allelic heterogeneity and specific genetic variation as modifiers of these cancer risks. ACE will be characterized separately as described in aim 3, and we will exclude probands with ACE rather than germline TP53 mutations from Aim 1 and 2 analyses. These studies will improve our ability to distinguish between germline TP53 variants and those associated with ACE, and the genotype-phenotype correlations elucidated will better define the TP53-associated tumor spectrum and cancer risks to help refine clinical management recommendations for both groups.